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1.
We studied the effects of winter water drawdowns (2.3 m) on beavers in Voyageurs National Park, Minnesota, USA. Our study
was designed to sample areas within the park that differed in water drawdown regime. Lodges were counted and beavers were
livetrapped and radio-implanted to study behavior, movements, and mortality. Active beaver lodge density, determined by aerial
survey in 1984 and 1986, was greatest along the shoreline of the drawdown reservoir. In winter beavers living on the drawdown
reservoir spent less time inside their lodges than did beavers from stable water environments, foraged more above ice, and
they were unable to fully use stored food. Only one case of starvation in the drawdown reservoir was documented, but beavers
in reservoirs that were drawn down survived winter in poorer condition than did beavers living in areas in which water levels
remained high. In spite of an increasing population and lack of widespread mortality, winter water drawdowns did alter beaver
behavior. To reduce these impacts, total annual water fluctuation should not exceed 1.5 m, and winter drawdown should not
exceed 0.7 m. Possible management alternatives and costs are discussed. 相似文献
2.
James M. Omernik David P. Larsen Christina M. Rohm Sharon E. Clarke 《Environmental management》1988,12(6):815-825
A map of summer total phosphorus in lakes has been compiled for Minnesota, Wisconsin, and Michigan to clarify regional patterns in attainable lake trophic state. Total phosphorus was used as a measure of lake trophic state because: (1) phosphorus plays a central role in controlling the overall fertility of most lakes, (2) total phosphorus values are available for a great number of lakes, and (3) phosphorus is measured in a consistent manner. The maps were compiled using patterns of total phosphorus data and observed associations between these data and geographic characteristics including physiography, land use, geology, and soils. Regions depicted on the map represent areas of similarity in phosphorus concentrations in lakes, or similarity in the mosaic of values, as compared to adjacent areas. Within each region, differences in total phosphorus can be compared to natural and anthropogenic factors to determine the types of lakes representative of each region, the factors associated with differences in quality, and the realistically attainable phosphorus levels for each type of lake. 相似文献
3.
James M. Omernik Christina M. Rohm Richard A. Lillie Nancy Mesner 《Environmental management》1991,15(2):281-293
A map of summer total phosphorus in lakes was compiled recently for a three-state area of the upper Midwest for purposes of
identifying regional patterns of total phosphorus in lakes and attainable lake trophic state. Spatial patterns in total phosphorus
from approximately 3000 lakes were studied in conjunction with maps of geographic characteristics that tend to affect phosphorus
balance in lakes to identify regions of similarity in phosphorus concentrations in lakes or similarity in the mosaic of values
as compared to adjacent areas. While degrees of relative homogeneity are apparent at many scales, the map was designed at
a scale that would yield regions with sufficient homogeneity to be useful for lake management throughout the area. In this
study, data from 210 lakes in a 1560-mi2 area in northwestern Wisconsin, sampled by the Wisconsin Department of Natural Resources in the spring of 1988 (subsequent
to the compilation of the phosphorus map), were examined to: (1) substantiate the existence of the regions depicted on the
map in northwest Wisconsin, (2) determine the nature and relative precision of the regional boundaries, (3) determine the
relative importance of natural and anthropogenic watershed characteristics, lake types, lake area, and lake depth in explaining
within-region differences in lake phosphorus, and (4) demonstrate how the regions might be used by local lake managers. 相似文献
4.
Long-term time-series data sets of two shallow Dutch lakes, Lake Veluwemeer and Lake Wolderwijd were subjected to ordination
and clustering by means of non-supervised artificial neural networks (ANN). Splitting of the data sets into sub-series corresponding
with three different management periods have allowed a comparative analysis of both the short-term seasonal and long-term
phytoplankton dynamics in relation to the restoration measures. The lakes were considered as hyper-eutrophic and have been
managed both with bottom-up and top-down management approaches. Results of the study have demonstrated that non-supervised
ANN allow to elucidate causal relationships of complex ecological processes (1) within the specific genus, Oscillatoria and Scenedesmus and (2) the combination of external nutrient control and in-lake food web manipulation of the two lakes achieved to control
eutrophication. 相似文献